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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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HTML 

              
                <h1>
  <span>Anchor</span>
  <span>Positioning</span>
</h1>

<div class="resizer"></div>
<div class="anchor" id="anchor">⚓️</div>
<div class="bubble" anchor="anchor" id="bubble"><div contentEditable>Hello!</div></div>

<div class="axis x" anchor="bubble">
  inset-inline = ?
</div>
<div class="axis y" anchor="bubble">
  <span>inset-block = ?</span>
</div>


<dialog open id="fallback">
  <p>Your browser does not support anchor positioning.</p>
  <p>To play with this demo, open it in Chrome Canary with the “Experimental web platform features” feature flag on.</p>
  <p>Here is a screen recording of this demo:</p>
  <video controls muted playsinline preload="none" poster="https://kizu.dev/videos/anchor-cover-dark.jpg">
    <source src="https://kizu.dev/videos/anchor-cover-dark.mp4" type="video/mp4" media="(prefers-color-scheme: dark)">
    <source src="https://kizu.dev/videos/anchor-cover-light.mp4" type="video/mp4">
    Sorry, your browser doesn’t support embedded videos. You can <a href="https://kizu.dev/videos/anchor-cover-dark.mp4">download it</a>.
  </video>  
  <p><button type="button" onclick="fallback.close()">Close this dialog</button></p>
</dialog>
!

CSS 

              
                @import url('https://fonts.googleapis.com/css2?family=Playpen+Sans:wght@100..800&display=swap');

/* It is not necessary to use anchor positioning for this example, but why not? It is mostly intended as an illustration. */

.bubble {
  position: absolute;
  z-index: 1;
  inset-block-end: anchor(start);
  inset-inline-start: anchor(center);
  background: lightgreen;
  color: #000;
  display: grid;
  place-items: center;
  font-size: 3em;
  font-weight: 150;
  aspect-ratio: 1;
  padding: 0.25em;
  border-radius: 50%;
  rotate: 7.5deg;
  transform-origin: 0 100%;
  border-end-start-radius: 0;
  box-shadow: 0.1em 0.2em 0.3em var(--shadow);
  
  /* Just for fun: a fallback via scroll-driven animations,
     because — why not? */
  animation:
    --top-overflow linear both,
    --right-overflow linear reverse both;
  animation-timeline:
    view(),
    view(inline);
  animation-range:
    exit 0 exit 155px,
    entry 0 entry 180px;
  
  & > div {
    rotate: -45deg;
    translate: -0.1em 0.1em;
  }
}

@keyframes --top-overflow {
  to {
    rotate: 87.5deg;
  }
}

@keyframes --right-overflow {
  to {
    rotate: -92.5deg;
  }
}


.anchor {
  position: relative;
  z-index: 1;
  font-size: 5em;
  rotate: 22.5deg;
  transform-origin: 50% 5%;
  line-height: 0.95;
  margin-inline: -0.5em;
  margin-block-end: -1lh;
  grid-area: --middle;
  text-shadow: 0.05em 0.1em 0.1em var(--shadow);  
}

.axis.y {
  position: absolute;
  inset-block: 0;
  inset-inline-end: anchor(start);
  border-inline-end: 2px dashed lightblue;
  padding-block: 1em;
  letter-spacing: 0.05em;
  
  & > span {
    display: inline-block;
    rotate: 180deg;
    writing-mode: tb;
  }
}
.axis.x {
  position: absolute;
  inset-inline: 0;
  inset-block-end: anchor(end);
  border-block-end: 2px dashed lightblue;
  margin-block-end: -1px;
  padding-inline: 1em;
}

h1 {
  grid-area: --corner;
  font-weight: 200;
  font-size: clamp(1rem, 15vmin, 5rem);
  text-align: center;
  line-height: 1;
  width: min-content;
  rotate: -8deg;

  & > span {
    display: inline-block;

    &:first-child {
      anchor-name: --anchor;
    }

    &:last-child {
      anchor-name: --positioning;
      margin-left: -0.05em;
    }
  }
  &::after {
    content: "✈︎";
    position: absolute;
    position-anchor: --anchor;
    inset-inline-start: anchor(end);
    inset-block-end: anchor(end);
  }
}

/* Page and resizer setup */

html {
  color-scheme: dark light;
}

body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  overflow: hidden;
  max-width: 100vw;
  --resizer-area: 1fr;
  grid-template:
    '--resizer . .' var(--resizer-area)
    '. --middle .' max-content
    '. . --corner' 2fr / var(--resizer-area) max-content 2fr;
  place-items: center;
  font-family: Playpen Sans, sans-serif;

  --shadow: #0005;
  
  @media (prefers-color-scheme: dark) {
    --shadow: #000;
  }
}

body:has(.resizer[style]) {
  --resizer-area: max-content;
}

.resizer {
  overflow: hidden;
  resize: both;
  width: 100%;
  height: 100%;
  grid-area: --resizer;
  position: relative;
  z-index: 2;
  
  &:not(:hover, :active) {
    opacity: 0;
  }
}

dialog {
  z-index: 9;
  outline: 200vmax solid #1238;
  overflow: auto;
  max-height: 100vh;
  box-sizing: border-box;  
}

video {
  max-width: 100%;
  max-height: 100vh;
  width: 1022px;
  height: 540px;
}

@supports (anchor-name: --foo) {
  dialog {
    display: none;
  }
}
!

JS
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